1. Field of the Invention
The invention relates to an irrigation control system destined to ensure that the quantity of water applied during irrigation of a given planted area represents the correct amount needed to rewet the soil profile to a predetermined maximal depth. Under normal conditions this maximal depth is the soil depth in which 85% of the active plant roots are present. The invention relates particularly to a control system capable of automatically stopping an irrigation cycle as soon as the wetting front reaches a depth above the final predetermined depth, from where the water will continue to drain and percolate down to the required depth containing the plant roots. It relates furthermore to a system adapted, under certain conditions, to start irrigation automatically whenever the water content distribution with depth should drop below a predetermined value.
2. Description of the Related Technology
In semi-arid countries with no rainfall during several months of the year artificial irrigation has been practiced for thousand of years. In modern times, when irrigated areas are rapidly increasing because of the increasing demand for fruits and vegetables and owing to urbanisation and industrialisation, water resources for irrigation are becoming scarce, and farmers are under pressure to use the available water frugally to the best advantage. Presently, the farmer is lacking the means to assure that the amount of water he applies in an irrigation is actually the amount needed to rewet the soil profile to the desired depth. In the recent past, various equipment has been designed for automatic irrigation, actuated by the sensed soil water content and/or by electronic timing. They include soil humidity sensors such as tensiometers or resistance blocks which are driven into the soil down to a depth at which the roots are most active and which emit signals for starting irrigation whenever the soil water content or soil water potential drop below a predesignated level. Another way of starting irrigation is by means of electronic timers which actuate valves or pumps after a predesignated time interval measured from the last irrigation. Both methods lack the means for stopping the irrigation process as soon as the quantity of water applied to the soil is sufficient to rewet the soil profile, and usually result in over-irrigation and waste of water resources.